Well I'm not gay. I dont care about the wanna be "wholesome" cringe stuff you said that Luffy embodies. I love the world building and the cast of One Piece - more the political and warfare side of it. So for me it would be undoubtedly better if Dragon, a badass mature character with much deepness and big ambitions (and certainly not childish ones), would be the MC of the story, and One Piece as a whole more focused on the ploitical and warfare part. Basically if the core of the story was similar to Kingdom in a sense of story telling and story building.
I know that most of the current One Piece fans love One Piece because it is a Shonen and because it is so childish with such a neg IQ and childish Straw Brain MC. The majority of current One Piece fans are either children or childish, escpially those who dont criticise the whole post TS story writing or Luffy as the MC. Its a typical Shonen which means it targets espcially those parts of the Anime fandom. Doesent change the fact that for me One Piece would be much better and potentially goated if it was like I described.
"Well I'm not gay". Amazing, smart way to start.
I will be quick here. There are three stages on developing an adult criterion. First, teens think of themselves as grown ups and get obsessed with edgy, half-assed works they feel to be "deep", "mature", "dark", etc. Then comes immature adults, who aren't anything but post-teens that resignify their pretentious tastes as what non-childish things are supposed to be (usually overrating anything that feels rebelious, politic and warfare, funnily enough considering what you said). And finally you have the proper adults with a properly mature understanding of thigns whose judgement is wide enough to appreciate works in their context. What truly defines not being childish in mentality isn't reacting against "gay", "cringe" stuff while embracing cheap politics, revolutions, wars... carried by an unidimensional character who hasn't even appeared in a whole chapter if we put together all his panels; but being capable of appreciating the quality of something according to its own terms.
One Piece wouldn't be much better and potentially goated if it was like you described. It would be pretentious, edgy crap losing almost everything that actually defines it as a piece of work. From day one this was about a character designed after a little kid seeking a fantasy dream and laughing at everything. A story about Laugh Tale, about Joy Boy, about a main character born in Children's Day, about a clan dying with a smile. And while it isn't perfect, and criticism is legit, what you are doing is asking for the moon because you probably don't even like what
One Piece is as a whole piece of work but whatever isolated part of it you want to see developed in a way that doesn't fit the rest of this manga at all.
Your version of
One Piece would be a mess without personality, without a thematic thread and without anything that actually makes this story the way it is. It is okay for it to be childish and we should criticize it in the context of being better or worse at it because that's its foundation and it would never work as whatever pseudo-mature "seinen" for nihilist teens you'd want it to become since it would mean losing said foundation.
This isn't
Kingdom, this doesn't need to be similar
Kingdom and this can't work if similar to
Kingdom without stopping being
One Piece.